ABX3 perovskite particles and their application in reverse mode controlling photo-flux

ABSTRACT

The present invention provides a reverse mode light valve containing ABX 3  perovskite particles; more specifically is related to a light valve containing halide ABX 3  perovskite particles that can control light transmittance. This light control valve has the property of higher light transmittance when the power is turned off (OFF state) and lower light transmittance when the power is turned on (ON state). In the halide ABX 3  perovskite particles, A is at least one of Cs + , CH3NH3 + , and Rb + , B is at least one of Pb 2+ , Ge 2+ , and Sn 2+ , and X is at least one of Cl − , Br − , and I − . This halide ABX 3  perovskite particles were suspended in a liquid suspension to make a light valve with a light transmittance control. This light valve performs well and opens up a completely new field of application for ABX 3  perovskite materials.

TECHNICAL FIELD

The present invention is related to ABX₃ perovskite particles and a reverse mode light valve; more specifically is related to the halide ABX₃ perovskite particles and a reverse mode light control valve that can control the light transmission. The light control valve has the property of higher light transmittance when the power is turned off (OFF state) and lower light transmittance when the power is turned on (ON state), and such a device is preferably used for windows, lenses, or a light shutter such as a sunroof. The fascinating multifunctional smart windows exhibit promising features for a wide range of applications in buildings, airplanes, automobiles, etc. The present invention provides a new use for ABX₃ perovskite material. Moreover, this reverse mode light valve has the advantages of high safety and low power consumption compared with the normal mode light valve.

BACKGROUND ART

Technically, a light valve is a device that can regulate the amount of light passing through a media like a water valve that can control the water flow. Window shade can be viewed as a light valve too. However, in this invention, the light valve is referred a device which can electronically control the light transmittance, and such a device is also scientifically referred as an electrochromic device. Depending on science behind an electrochromic device, it can be further classified as polymer dispersed liquid crystal (PDLC) (U.S. Pat. No. 3,585,381), electrochemical device (EC) (U.S. Pat. No. 9,581,877) and suspension particles display (SPD) (U.S. Pat. No. 6,606,185).

In a typical light valve, it is general dark color and transmits less light through when the power is turned off (OFF state), and it becomes light color and transmits more light through when the power is turned on (ON state); such an electrochromic device is thus referred to a normal mode light valve. The reverse mode light valve manipulates the light in a reversed way as to that of the normal mode light valve, and it is light color and transmits more light through when the power is turned off (OFF state) and becomes dark color and transmits less light through when the power is turned on (ON state). For the normal mode light valve which is less transparent when power is off, implies that once the power supply system fails, there is less visibility between two sides of the device, this may cause an adverse situation in certain circumstances. For example, the passengers of the vehicle would be difficult to spot the hazard situation outside when the electrochromic window lose its electric power. Contrasting to a normal mode light valve, the reverse mode light valve is more transparent at an OFF state, this eventually avoids the visibility problem in case of a power failing. Furthermore, passengers in most time need visibility for driving and for sightseeing, so the light valves (electrochromic windows here specifically) need to be transparent. To maintain this long period transparency, a normal mode light valve would require to be powered ON all the time, but a reserve mode light valve would simply be in OFF state without the need of power supplying. Obviously, the reverse mode light valve would provide energy saving most time comparing to the normal mode light valve.

Considering above merits of safety and energy saving, the reverse mode light valve should be highly demanded in applications, however, the development of such a reverse mode light valve is still a scientific challenge. Of a few reports related to reverse mode light valves found in prior arts, such as CN201710186038.6, WO/2015/022980, CN201420849573.7, U.S. Pat. No. 6,383,577, and the article published in Japanese Journal of Applied Physics, L557-L559, 43 (4B), 2004), they are all basing on polymer stabilized liquid crystal (PSLC) systems with very limited success.

This invention presents the method to use ABX₃ perovskite particles to control the flux of light in a reverse mode electrochromic device, i.e., a reverse mode light valve (r-LV for short hereafter). Specifically, in this invention, the reverse mode light valve is referred a device that the light transmittance can be controlled by alternating current (AC). This reverse mode is more transparent when the power is turned off (OFF state) and becomes less transparent when the power is turned on (ON state). Such a device with controllable light switching and energy-saving advantages can be used as smart windows for transportation vehicles, architect buildings and other places where the light transmittance to be electronically controlled.

Perovskite, the name of the perovskite, originated from the Russian geologist Perovski and originally single-pointed the calcium titanate (CaTiO₃) mineral. Later, crystals with similar structures were collectively referred to as perovskites. The cell structure of the halide ABX₃ perovskite referred to in this patent is shown in FIG. 4.

Among them, B atom and 6 X atoms form octahedral units, and 8 octahedral units occupy the position of the hexahedral apex centered on the A atom. This kind of material has a unique structure, giving it excellent optical, electrical, magnetic and thermodynamic properties, and is a new type of materials with attractive prospects.

In 2009, the ABX₃ perovskite material was first reported for solar cells (J. Am. Chem. Soc. 131, 6050-6051, 2009). “Science” rated perovskite solar cells as one of the top 10 scientific breakthroughs in 2013. In January 2018, the Swiss Federal Institute of Technology in Lausanne set a new world record efficiency of 23.25% for a perovskite solar cell. In addition, the ABX₃ perovskite material has been explored in other potential applications, such as LED (Light Emitting Diodes) (Tan, Zhi-Kuang, et al., Nature Nanotechnology, 9: 687-692, 2014), Lasers (Haiming Zhu, et al., Nature Mater., 14: 636-642, 2015), Photodetectors (Zhenqian Yang, et al., Adv. Materials, 30(8):1704333, 2018), Memristors (Zhengguo Xiao, et al., Advanced Electronic Materials, 2(7): 1600100, 2016), Photocatalytic (Sunghak Park, et al., Nature Energy, 2, 16185, 2016), Thermochromic (Jia Lin, et al., Nature Materials, 17, 261-267, 2018), and Ferroelectrics (Heng-Yun Ye, et al., Science, 2018, 361, 151-155).

Can ABX₃ perovskite material be used to make a reverse mode light valve? No report related this application has been found in prior arts. Therefore, being the first time, the present invention discloses a technology how to use ABX₃ perovskite particles to make a reverse mode light valve, and is opening a new application field for ABX₃ perovskite materials.

SUMMARY OF THE INVENTION

This invention presents the method to use ABX₃ perovskite particles to control the flux of light in a light control device (referred as a light valve). The present invention provides a new use of the ABX₃ perovskite material, and method to make such a material. More specifically, the present invention further provides a reverse mode light valve(r-LV). This invented r-LV device comprises a liquid suspension having such a material of ABX₃ perovskite particles, which can electronically control transmission of light in such way that it allows more light transmitted through when the power is turned off (OFF state) and less light transmitted through when the power is turned on (ON state). Still, ABX₃ perovskite particles with a more specific chemical composition is specified, where A is at least one of Cs⁺, CH3NH₃ ⁺, and Rb⁺, B is at least one of Pb²⁺, Ge²⁺, and Sn²⁺, and X is exclusively selected from one of halide anions including Cl⁻, Br⁻, or I⁻. As such a specified composition, the said ABX₃ perovskite material is referred as halide ABX₃ perovskite material. According to this invention, the referred halide ABX₃ perovskite material is to be used in a form of particles, thus more specifically these particles used are referred as halide ABX₃ perovskite particles. Still according to the invention, these halide ABX₃ perovskite particles are characterized in that have a non-spherical morphology. Still further, the halide ABX₃ perovskite particles morphology is at least one of a nanorod (one-dimensional); a nanosheet (two-dimensional); a cuboid, irregular (three-dimensional).

According to this invention, the liquid suspension, which is used as a liquid medium to suspend the ABX₃ perovskite particles, comprises one or more a mineral resistive material, a synthetic resistive material, and a vegetable oil.

According to this invention as illustrated in FIG. 1, the said transparent electrode (100) can be made of the same material or different materials, where light can be transmitted through, preferably having a light transmittance equals to or greater than 80%.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 presents schematically the r-LV, wherein, a liquid suspension (300) is sandwiched between two transparent substrates (100) and (100). The halide ABX₃ perovskite particles (200) are suspended in the liquid suspension (300).

FIG. 2 presents light transmittance of a r-LV device made according to this invention Example 6 before and after applying an electric voltage of 220V.

FIG. 3 presents SEM image of CsPbBr₃ nanosheets according to this invention Example 3.

FIG. 4 presents the cell structure of the ABX₃ perovskite.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a new use for halide ABX₃ perovskite particles to control the flux of light in a light control device in a reverse mode, thus referred as a reverse light valve (r-LV).

FIG. 1 schematically illustrates a typical r-LV device, wherein, a liquid suspension (300) is sandwiched between two transparent substrates (100) and (100). The halide ABX₃ perovskite particles (200) are suspended in the liquid suspension (300). In the absence of an applied electrical field (OFF state), the halide ABX₃ perovskite particles in the liquid suspension assume random positions due to Brownian movement. Hence, the beam of light passing into the light valve is partially absorbed/scattered, other part of light transmits through the light valve, so the light valve is thus relatively bright and transparent in the OFF state. When an electric field is applied thereto (ON state), the light control halide ABX₃ perovskite particles are polarized, that the effective maximum surface of the ABX₃ perovskite particles is perpendicular to the direction of the electric field. Hence, a major part of light going into the light valve is absorbed/scattered, and other smaller fraction of light is transmitted through, so the light valve is thus relatively darker and less transparent in the ON state.

Therefore, being the first time, the present invention provides a novel use of the ABX₃ perovskite particles in a reverse mode light control device (r-LV). According to the present invention, the invented r-LV comprises a liquid suspension having such a material of ABX₃ perovskite particles, which can electronically control transmission of light in such way that it allows more light transmitted through when the power is turned off (OFF state) and less light transmitted through when the power is turned on (ON state). Still, ABX₃ perovskite particles with a more specific chemical composition is disclosed, where A is at least one of Cs⁺, CH3NH₃ ⁺, and Rb⁺, B is at least one of Pb²⁺, Ge²⁺, and Sn²⁺, and X is at least one of halide anions selected from Cl⁻, Br⁻, or I⁻. Accordingly, the specified ABX₃ perovskite material is referred as halide ABX₃ perovskite material. According to this invention, the referred halide ABX₃ perovskite material is to be used in a form of particles, thus more specifically these particles used are referred as halide ABX₃ perovskite particles. Still according to the invention, these halide ABX₃ perovskite particles are characterized in that have a non-spherical morphology. Still further, the halide ABX₃ perovskite particles morphology is at least one of a nanorod (one-dimensional); a nanosheet (two-dimensional); a cuboid, irregular (three-dimensional).

As illustrated in FIG. 1, the said ABX₃ perovskite particles (200) which are encapsulated inside the said liquid suspension (300) shall be capable of re-orientating themselves in an electronic field. Therefore, the geometric dimension of the said ABX₃ perovskite particles needs to be scientifically optimized. According to the invention, the said ABX₃ perovskite particles preferably to be in a form of flakes and referred to nanosheets herein. Still the said nanosheets are preferably having a length of about 50 nm-2000 nm, more preferably 200 nm-500 nm, and a thickness of 5 nm-100 nm, more preferably 10 nm-50 nm.

According to the invention, the said ABX₃ perovskite particles shall have such a characteristic that the said ABX₃ perovskite particles are capable of being polarized under an electric field, and still the effective maximum surface of the polarized ABX₃ perovskite particles is perpendicular to direction of the electric field. In one embedment, the said ABX₃ perovskite particles are nanosheets, after being polarized under an electric field, the surface of the large specific surface of the nanosheets is oriented to be perpendicular to the direction of the electric field.

According to this invention, the said liquid suspension (300), which is used as a liquid medium to suspend the ABX₃ perovskite particles, comprises one or more non-aqueous, electrically resistive liquids. Such a liquid or a liquid mixture, referring as the suspension medium, can maintain the suspended ABX₃ perovskite particles in gravitational equilibrium.

More specifically in this invention, the liquid suspension (300) comprises one or more a mineral resistive material, a synthetic resistive material, a vegetable oil. Mineral resistive materials, such as transformer oils; synthetic resistive materials, such as silicone oils, fluorocarbon organic compounds, plasticizers (such as Dioctyl phthalate, Dibutyl phthalate, Diisobutyl phthalate, Triisodecyl trimellitate (TDTM) etc.), dodecylbenzene, polybutene oil, etc.; vegetable oils, such as castor oil, soybean oil, rapeseed oil, etc., are good liquid suspension mediums. As a broad scope, the liquid suspension medium used in the light valve of the present invention can be any liquid light valve suspension known in the art and can be formulated according to techniques well known to those skilled in the art.

According to this invention as illustrated in FIG. 1, the said both transparent electrodes (100) can be made of the same material or different materials, where light can be transmitted through, preferably having a light transmittance equals to or greater than 80%, more preferably 90%. Either one or both the said transparent electrodes (100) can be ITO conductive glass, ITO/PET conductive film, Ag nanowire/PET conductive film, Cu nanowire/PET conductive film. The transparent electrodes (100) are preferred to be of the same material for the simplicity of processing and for the same physical properties (such as flexibility and thermal expansion), important for device durability under certain conditions, such as thermal stress.

Since the halide ABX₃ perovskite particles are sensitive to moisture and oxygen, the liquid suspension containing the said halide ABX₃ perovskite particles sandwiched between the two transparent electrodes is preferably to be sealed with a resistive material, such as epoxy resin, etc. An alternating current is thus applied through the transparent electrodes (110) to control the light transmittance through the assembled r-LV, and the voltage of such an alternating current is preferably in the range of 5-500 V, more preferably in a range of 30-220 V, which can be easily achieved by a common transformer.

The invention will now be described in more detail with reference to the following examples. However, these examples are given for illustration only and are not intended to limit the scope of the present invention. All chemicals used in the examples are purchased from Sigma-Aldrich Company unless otherwise specified. In all these examples, all parts and percentages are by weight unless otherwise noted. The light transmittance and absorption spectrum of the r-LV device was measured by an Oceanview spectrometer.

EXAMPLE 1 Preparation of Cs-Oleate

Cesium carbonate (Cs₂CO₃, 4.07 g) was loaded into a 250 mL 3-neck flask along with octadecene (ODE, 50 mL) and oleic acid (11.088 g), and the mixture was dried for 1 h at 120° C. and then heated under Argon (Ar) to 150° C. until all Cs₂CO₃ reacted with oleic acid. The obtained Cs-Oleate may precipitate out of ODE at room temperature, and it can be preheated to make it soluble before further using.

EXAMPLE 2 Synthesis of CsPbI₃ Nanosheets

N,N-dimethylformamide (DMF, 100 mL) and lead iodide (PbI₂, 2.305 g) were charged into a 250 mL flask. Oleic acid (0.438 g) and octylamine (2.339 g) were added. After complete solubilization of PbI₂, 5 mL Cs-Oleate solution was added (prepared as described in Example 1). Then, the resulted solution was added into a 5 L flask along with 4200 mL of toluene. Subsequently, the resulted solution was centrifuged at 5000 G for 1.5 hours and the supernatant was discarded to yield the light control CsPbI₃ nanosheets. Finally, the CsPbI₃ nanosheets were further dispersed with 500 mL of toluene, mixed well with shaking and sonication (referring as LCP-Example-2).

EXAMPLE 3 Synthesis of CsPbBr₃ Nanosheets

In the same manner as in Example 2, but 1.835 g of PbBr₂ was used instead of 2.305 g of PbI₂. A toluene mixture containing CsPbBr₃ nanosheets is obtained and referred as LCP-Example-3. FIG. 3 presents SEM image of CsPbBr₃ nanosheets.

EXAMPLE 4 Preparation of r-LV Suspension Containing CsPbI₃ Nanosheets

Into a 250 mL round bottom glass flask was weighted 10 g of Triisodecyltrimellitate (TDTM), then the LCP-Example-2 prepared in the Example 2 was added in portions. After thoroughly mixing the resulted suspension by shaking, toluene was subsequently removed by a rotary evaporator for 3 hours at 80° C. to yield a r-LV suspension containing CsPbI₃ nanosheets, which is referred as r-LV Suspension Example-4.

EXAMPLE 5 Preparation of r-LV Suspension Containing CsPbBr₃ Nanosheets

Into a 250 mL round bottom glass flask was weighted 10 g of silicone oil, then the LCP-Example-3 prepared in the Example 3 was added in portions. After thoroughly mixing the resulted suspension by shaking, toluene was subsequently removed by a rotary evaporator for 3 hours at 80° C. to yield a r-LV suspension containing CsPbBr₃ nanosheets, which is referred as r-LV Suspension Example-5.

EXAMPLE 6 r-LV Devices Made from r-LV Suspension—Example-4

In this example, a layer of the r-LV Suspension—Example 4 made in Example 4 at a thickness of 200 um was sealed between two transparent electrodes of ITO conductive glass using epoxy resin to produce a light valve referring as r-LV Device-6. When no electric voltage was applied (OFF State), r-LV Device-6 exhibited an orange tint and light transmission was measured to be 19.4%. When it was electrically activated using 220 Volts AC at 50 Hz (ON State), the r-LV Device-6 became darker and light transmission was measured to be 7.0% only. Table 1 summaries these results. Further, FIG. 2 presents the absorption spectrum of r-LV Device-6 at OFF state and ON state respectively.

EXAMPLE 7 r-LV Devices Made from r-LV Suspension—Example-5

In this example, a layer of the r-LV Suspension—Example 5 made in Example 5 at a thickness of 180 um was sealed between two transparent electrodes of ITO conductive glass using epoxy resin to produce a light valve referring as r-LV Device-7. When no electric voltage was applied (OFF State), r-LV Device-7 exhibited an orange tint and light transmission was measured to be 25.1%. When it was electrically activated using 220 Volts AC at 50 Hz (ON State), the r-LV Device-7 became darker and light transmission was measured to be 12.5% only as listed in Table 1.

TABLE 1 Typical performance of r-LV devices Transmittance % Example r-LV Device Off state On state Example 6 r-LV Device-6 19.4 7.0 Example 7 r-LV Device-7 25.1 12.5 

What is claimed is:
 1. A reverse mode light valve, comprising of a first layer of a transparent conductive substrate; an active layer containing an ABX₃ perovskite particles are suspended in a liquid suspension; and a second layer of transparent conductive substrate.
 2. The reverse mode light valve as recited in claim 1, wherein the said the reverse mode means the light control valve has the property of higher light transmittance when the power is turned off (OFF state) and lower light transmittance when the power is turned on (ON state).
 3. The reverse mode light valve as recited in claim 1, wherein the said ABX₃ perovskite particles are halide ABX₃ perovskite particles, and wherein A is at least one of Cs⁺, CH3NH₃+, and Rb⁺, B is at least one of Pb²⁺, Ge²⁺, and Sn²⁺, and X is at least one of Cl⁻, Br⁻, and I⁻.
 4. The halide ABX₃ perovskite particles as recited in claim 3, wherein the said ABX₃ perovskite particles, and wherein A is at least one of Cs⁺ and CH3NH₃ ⁺, B is Pb²⁺, X is at least one of Br⁻ and I⁻.
 5. The ABX₃ perovskite particles as recited in claim 1, wherein the said ABX₃ perovskite particles have a non-spherical morphology.
 6. The ABX₃ perovskite particles as recited in claim 5, wherein the said ABX₃ perovskite particles morphology is at least one of the nanorod (one-dimensional); a nanosheet (two-dimensional); a cuboid, irregular (three-dimensional) particles.
 7. The ABX₃ perovskite particles as recited in claim 6, wherein the said ABX₃ perovskite particles morphology is nanosheets have a length of about 50 nm-2000 nm, and a thickness of 5 nm-100 nm.
 8. The reverse mode light valve as recited in claim 1, wherein the said light valve means that said halide perovskite particles are uniformly dispersed in a liquid suspension.
 9. A liquid suspension as recited in claim 8, wherein the said liquid suspension can maintain the suspended ABX₃ perovskite particles in gravitational equilibrium.
 10. A liquid suspension as recited in claim 8, wherein the said liquid suspension comprises one or more a mineral resistive material, a synthetic resistive material, a vegetable oil.
 11. A liquid suspension as recited in claim 8, wherein the said liquid suspension is sandwiched between two transparent electrodes. 